The problem is we have no idea about who the seller is and what she may well of done to resolve the situation. We have no idea how old the "children" are as they may well be a proportion of older teenagers...
As for the "one with a problem", if they had not had a dog before, the situation could go either way..... I fully admit that we brought home 2 rescue dogs and sadly I had to return them almost immediately as my "problem" son could not cope with the exuberance of the first, (and the second would of ripped the cat to pieces due to a history not revealed by the rescue till later).
I would rather see someone ask a nominal fee for the dog in the hope that the purchaser is demonstrating being able to also afford to care for the dog rather than a freebie. We're also increasingly hearing about rescues having such a long waiting list that they could of tried and looking at options.
The existing dog is quite possible a more sedate dog. Ok maybe she under-estimated the amount of time needed for a working cocker, but perhaps that could also be the fault of the breeder who didn't stress that...
Lots of ifs', buts and may-be's and IMO perhaps we shouldn't be so quick to judge